Valve spindles are integrated in combustion engines to control the flow of air and exhaust gases to and from the cylinders of the engine.
Modern two-stroke diesel engines are subjected to increasing environmental demands regarding the emission of gases, such as CO, NOx and sulphur. To meet these demands and to reduce emissions, the combustion temperatures have been increased in the engine. This has in turn led to increasing corrosion of the engine's components, in particular, the exhaust valve spindle.
Valve spindles are typically forged from medium carbon construction steels and to increase their resistance to corrosion, the valve spindle's valve disc may be provided with a corrosion resistant cladding. Initially, the cladding was welded to the valve disc. However, in recent development the corrosion resistant cladding is applied in the form of a metallic powder to the valve spindle by Hot Isostatic Pressing (HIP). In order to prevent diffusion of carbon from the valve disc to the corrosion resistant cladding, a buffer layer of low carbon steel is applied directly onto the forged valve disc prior to application of the cladding.
WO2010/083831 shows an example of a forged valve spindle which comprises an outer cladding of a corrosion resistant material and a buffer layer that has been applied onto the valve spindle by HIP. The valve spindle further comprises a valve seat which is integrated in the upper surface of the valve disc.
One problem with known valve spindles is that carbon may diffuse from the forged steel material into the seat of the valve spindle. Carbon may reduce the ductility and the corrosion resistance of the seat material and thereby reduce the life time of the valve spindle.
Another problem associated with the known valve spindle is that the powder materials of the buffer layer may blend into cladding powder and cause a zone of mixed buffer- and cladding powders in some areas of the valve spindle. In the periphery of the valve disc, severe corrosive conditions exist during operation of the engine. In this area contamination, such as carbon, from the buffer material may reduce the resistance of corrosion of the cladding material to an extent where the lifetime of the valve spindle is reduced.
A further drawback in the manufacture of the known valve spindles is that the manufacturing process is complicated and involves several subsequent Hot Isostatic Pressing steps.
Hence, it is an object of the present invention to solve at least one of the problems of the prior art. In particular, it is an object of the present invention to achieve a simple and cost effective method for manufacturing a valve spindle, which spindle may sustain long term use without failure. A further object of the present invention is to achieve a valve spindle which may sustain long term use without failure.